Electric contact structure



Nov. 24, 1931. I A. M. PONIATOFF 1,833,757

ELECTRICAL CONTACT STRUCTURE Filed Feb. 7, 1930' Z 3 .37 6 I /a a H z/ H His Atto-r nex Patented Nov. 24, 1931 UNITED STATES I. PONIA'I'OI'F, OI PHILADELPHIA, PENNSYLVANIA, ASBIGN OR 'ro GEN- ERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK ALEXANDER PATENT; OFFICE- EEO'I'RIOAL CONTACT STRUCTURE Application fled rem-um r, 1930. Serial 110. 420,619. a

My invention relates to electrical contact structure, and more particularly to contact structure for switches of the large capacity, fluid-break type. a

5 In circuit mterrupters of large current carrying capacity, the dissipation'of heat due to comparatively high resistance at the contacting surfaces presents a serious difiiculty in switch desi In order to prevent the switch from running hot at its normal rated capacity, it is necessary to provlde either an elaborate cooling system or to keep the resistance at the contacts within certain limits. I This resistance may result from a number of causes, some of the more important being insufficient contact pressure and the formation of high resistance oxides on the contacting surfaces.

It is an object of my invention to provide an improved switch contact structure for maintaining the resistance, and consequently the heating, at the switch contacts within comparatively low limits thereby increaslng the effective current carrying capacity of the switch.

'It is a further object of my inventlon to provide an improved switch contact structure for maintaining a substantially constant bearing pressure between the contact surfaces of the switch and for precluding the formation ofhigh resistance oxides at said surfaces, a

It is a further object of my invention to provide an improved switch contact whichshall be simple and easily constructed, and

which shall present a low resistance path for current traversing the same.

My inventionwill be morefully set forth in the following description, referring to the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawings, Fig. 1 is an elevational view, partly in section, of circuit interrupting apparatus embodying my invention; Fig. 2 is an enlarged view, partly 50 in section, of structure illustrated in Fig. 1,

and Fig. 3 is a view taken alongthe line 3-3 of Fig. 2. Fi 1 il ustrates a circuit interrupter of the uid-break type comprising a tank or housing 1 for containing an insulating and arc-extinguishing medium 2, such as oil, within which the movable parts of the switch structure are immersed. The terminal or stationary part of the switch structure comprises a pair of conductor studs 3 mounted .within and secured with respect to the to wall of an upper section 1 of the switc housing. The usual insulating bushin s 4 serve to insulate the conductor studs rom the circuit breaker housing, and the bushings are in turn secured in any suitable manner, as by the clamping flanges' l', to the housin The conductor studs 3 are hollow and provi ed with ventilating tubes 5 for removing heat from the interior of the studs, this arrangement being described and claimed in my copending application Serial No. 426,67 7 filed February 7, 1930, forming no part of the present lnvention.

- Mounted and electrically connected to the lower end of each conductor stud 3 is the stationary contact structure of the switch, the same bein disposed beneath the oil level as illustrate The lower end of the conductor stud comprises a pair of flange-like ,brtions 6 at opposite sidesof the tubular stu at the end of which a V-shaped slit or notch is formed. This construction permits the switch contact structure to be connected directly to the conductor stud without the usual adapter generally interposed between the conductor stud and contact. Due to the fact that the adapter introduces additional resistance in the switch structure and increases the construction costs, the elimination thereof is tion. 'In the present instance the laminae are solidified to form a uniformly conducting portion by first tin-plating, or otherwise coating with a suitable brazlng metal, each individual lamina throughout its length correspondingto the length of the portion to be solidified, andthereafter applying pressure to compress the laminae in the presence of heat. The heat for the brazing process may be applied-either bypassing an electric current through the laminae tobe brazed or by placing the same within a vacuum furnace,

' the pressure, of course, being maintained.

7 beapparent at this-point that other suitable processes or'methodsfor producing a solid, "uniformlyconducting section at the opposite endszofthe laminae may be employed. The solid ortions 9'and 10 are secured and electricali y connected to the flanges 6 of the conductor stud in any suitable manner, as by the clamping plates 11 and through bolts .12. A spacing member 13 is mounted between the flanges 6 and serves as a guide for a rod 14 freely 'slidable therein, and secured at its lower end, as by screw-threaded engagement to a pressure 'plate15. Resilient-means, as a coil spring 16, is seated within the loop at one end on stationary structure of the conductor-stud and serves to bias the pressure plate 15 against-the inner side of the loop contact so as to exert an expansive action thereon. A stop or limit nut 14: is carried by the rod 14 to maintain the movement thereof within predetermined limits.

Asection of the laminae comprising the loop substantially opposite the pressure plate 15 is likewise brazed or suitabl treated to produce asolid, uniformly con ucting portion 17 to which a contact plate 18 is pressure brazed as in the manner previously described. The pressure plate 15 may be connected to the inner portion of the loop in any suitable manner as by the screws 19, 1

The contact plate 18 is preferably electri- Lcally' connected to thefportion 17 by brazing so that it. forms a substantially integral and uniformly conducting part thereof, thereby reducing the resistance of the union. The

" contact, plate is of materialwhose oxide has i a lower resistance than the oxide of the materialcompris'ing the laminae of the loop contact-5 In. the presentdnstance the material of the contact-plate is of silver whose oxide is of considerably lower resistance' than the copper .oxide of the laminae 8., The con-- .tactjplate Bi -preferably flat, and as illus- When the contact surfaces are veryclose together and separated only by the oil' film,

- the film is broken by arcing between the contacts, thereby establishing the current. Since it is essential that the duration of this areing be decreased to a minimum in order to reduce burning of the contacts, the oil film should be gotten rid of as quickly as possible so that the contacting surfaces may be brought together in metallic engagement with each other. In the present instance the oil film flows 'outfrom between the contacting surfaces very quickl during closure of the contacts so that burning of thesurfaces thereof is minimized. I

The coacting contact of the switch comprises a bridging member 20 adapted to be raised or lowered by, suitable means withinthe switch housing by an operating rod 21, and having at its opposite ends a contact plate 22 secured and electrically connected thereto in any suitable manner and correspondin in material and construction with its coacting butt contact 18. It will be apparent that the copper laminae may be formed as a continuous loop, in which case the portion of the loop opposite the contact portion would be brazed or otherwise solidified to form a uniformly conducting portion for suitable connection with aconductor stud.

The contact structure abovev described not only provides a low resistance path for current passing from the conductor stud to the solidified portions 9 and 10, the laminae 8 and the contact portion 17, but permits the use of resiliently biased, flexible structure so that the pressure between the coacting contact surfaces may be maintained substantially constant, thereby maintaining the resistance due to this factor substantially constant. The maintenance of constant contact pressure is not possible when the resiliency of the copper laminat-ions alone is depended upon. This is due to the fact that the resiliency of the copper varies with the temperature and in the ease of flat, spring-like laminations, as in the brush type of contact, for example, a permanent set may occur so that readjustment would be necessary in order to restore the proper contact pressure. The use of the silver contact plate serves to materially reduce the contact resistance since, as previously explained, the silver oxide the coaoting contact contacts in a downward direction. If it is which may form on the contact surface is of lower resistance than copper oxide and moreber 20, but. is dependent on the spring 16 whose tension may be adjusted in any suitable V manner.

When the switch is traversed by heavy short circuit currents or overloads, the bridging member 20- is acted upon by electromagnetic forces tending to repel the movable desirable for the switch to remainclosed during these heavy currents, it is also desirable that the contact resistance shall not increase and that the contact pressure be maintained substantially constant. For the purpose of compensating for a certain amount of yielding of the mechanism holding the bridging member in its closed position, the compression spring 16 is adjusted to have an initial tension so that the contacts are maintained together at substantially constant pressure even though the bridging member is rep'elled to a certain extent by the forces set up by the heavy currents. In the same manner, during closing movement of the switch, the compression spring will provide substantially constant pressure; between the contact surfaces, practically from the time the movable contacts carried by the bridging member first engage the coacting contacts until they are disengaged therefrom.

It will be noted that the path of the current through the switch includes no high resistance unions such as where the current must flow transversely of the 'laminations. In each instance the electrical connection is between solid uniformly conducting portions, the intermediate flexible laminae affording equal resistance paths in parallel for the current. Engagement of the contact surfaces of the switch permits the contact surfaces to be pressed together so that the contact resistance may be roughly estimated from the actual contact area and the bearing pressure exerted by the spring 16.

It shall be understood that the term brazed as used in the specification and fol-. lowing claims, is to include any operation for merging the laminae at any portion of the loop into a solid, uniformly conducting section.

It shall be further understood that my invention is not limited to the specific details of construction and arrangement thereof herein illustrated, and that changes and modifica out departing fromthe spirit of my invento form a substantially solidconductor for electrically connecting the contact structure in a circuit, and a contacting (portion dis osed intermediate the ends of sai loop, sai contactmg portion comprising a brazed section of the laminae to form a substantially solid y r and uniformly conducting portion.

2. In, an oil circuit breaker, switch contact structure having large current carrying capacity comprising a plurality of leaf shaped laminar of conducting material in the form of an open loop, the sides of said loop being formed of the flexible laminae and the opposite ends of the loop and lower part thereof forming the contact surface being brazedtoform solid, uniformly conduct mg portions. V

3. In circuit interrupting apparatus, switchcontact structure having high current carrying capacity comprising a plurality of leaf-like laminae of conducting material arranged in the form of an open loop, the free ends of 7 said loop connected to terminal structure, and a contact-plateof material less subject to oxidation than that "of said conductingmaterial electrically connected to the laminae at an outer side of said loop forming a contact surface thereon.

4. In circuit switch contact structure com rising aplurality of leaf-like laminae o laminae brazed at one section to form a solid uniformly conducting portion, and a silver late electrically connected to said portion orming a contact surface onsaid laminaeinterrupting apparatus,

copper, said 5. In a circuit interrupting apparatus,

switch contact structure comprising a plurality of laminae of conducting material in the form of an open loop, the laminae at the opposite ends of said loop being brazed to form solid, uniformly conducting portions,

clamping means for electrically connecting f said portions to a'conductor stud, a silver contact surface at the outer side of said loop electrically connected to said laminae, a relatively movable silver contact surface co'acting therewith, and'a spring disposed within said loop for biasing the laminae toward said second contact surface thereby establishin substantially constant bearing pressure and electrical resistance between the I coacting contact surfaces. a

6. The combination with a fluid break switch comprising relatively movable con tact structure adapted to operate within an I insulating fluid, of means for maintaining the bearing pressure and electrical resistance between thepontacting surfaces of the switch substantially uniform comprising acontact member formed of laminae of conducting matcrial in the shape ofa loop,-the laminae at -one art of the loop being brazed to form a soli uniformly conducting portion, a silver vplate electrically connected to said portion at the outer side of said loop forming thereon a contact surface, av relatively movable silver contact surface coacting therewith, and a spring disposed within said loop for pressing together said contact surfaces at substantially constant pressure when the switch is in its closed circuit position. i

7. In a circuit breaker comprising relatively movable butt contacts, contact struc ture comprising a sheaf of laminae of conducting material in the form ofa loop connected at opposite ends to a conductor stud, a section of said loop being brazed to form a solid,

uniformly conducting portion having a butt contact surface on the outer side of said loop.-

In witness whereof, I have hereunto set In hand this 29th day of January, 1930.

ALEXANDER M. PONIATOFF. 

